1. Field of the Invention
This present invention relates to a portable communication apparatus, and more particularly, to a foldable and portable communication apparatus which can reduce the electromagnetic wave absorbed by users.
2. Description of the Prior Art
Mobile phones nowadays are very popular portable communication apparatuses. The American Federal Communications Commission (FCC) sets up standard criteria, the so called specific absorption rate (SAR), for the mobile phone or its apparatus. Other countries also set up similar standard criteria. SAR indicates the ratio of unit biomass to electromagnetic wave absorption. Under these standard criteria, in the prior art, the maximum SAR level of the ratio of head average unit mass to electromagnetic wave absorption cannot exceed a predetermined value while mobile phone cases radiate the maximum outputting power at normal usage position regarding to a mobile phone close to the head. SAR can be actually measured in a lab or computed by electromagnetic numerical analysis software.
For foldable mobile phones, the method to reduce SAR of the prior art can be generally separated into two kinds: changing the circuit impedance or changing the radiating power of the antenna. However, changing the circuit impedance involves complicated circuit design, and changing the radiating power of the antenna may affect communication quality. Both ways of changing the foldable mobile phone of the prior art to reduce SAR involves complicated design modification.
The efficiency of the radiating power of the antenna can be measured by effective isotropic radiated power (EIRP). In principle, when the communication distance is fixed, the bigger of the value of EIRP, the stronger the receiving signal, and the better the communication quality. In contrast, the same EIRP can exchange for farther communication distance or bigger covering range in the condition of the same communication quality and the same strength of receiving signal. When designing mobile phones, the EIRP must also be taken into consideration in addition to the fact that SAR should be reduced. In other words, the communication quality should be maintained while reducing the electromagnetic wave absorbed by users.
A foldable mobile radio equipment was disclosed in Japan patent No.2003-087375, which includes an upper case and a lower case. An antenna is disposed in the lower case and connected with the upper case by complicated machinery design. The major objective of the Japan patent is to avoid a situation in which radio wave reception sensitivity is reduced by antenna interference.
It is very important to reduce SAR and also take EIRP into consideration while designing the portable communication apparatus.